Many different types and variations of internal combustion engines, specifically engines for vehicles, have utilized turbochargers so as to increase the compression ratio and thereby increase the power generated by the engine. The turbocharger conventionally has the turbine section thereof driven by exhaust gases, with the turbine section driving a compressor section for increasing the pressure of the fuel-air mixture as supplied to the combustion chambers. The exhaust gas, after driving the turbine section, is normally discharged to the atmosphere in a conventional manner. While the use of turbochargers in this manner has proven desirable with respect to the ability of increasing the compression ratio, nevertheless this mode of operation also normally requires that an increased quantity of fuel-air mixture be supplied to the combustion chamber. This thus decreases the fuel efficiency of the engine, and also increases the quantity of undesired emissions in the exhaust gases. This operation also normally requires the use of higher octane fuel, and results in the engine running at a significantly higher temperature. The advantage of utilizing a turbocharger thus causes disadvantages which, in many instances, are of overriding importance so as to prevent the practical use of a turbocharger.
Accordingly, the present invention relates to a multi-cylinder internal combustion engine having an improved turbocharger arrangement associated therewith, which arrangement permits a portion of the exhaust gases to be resupplied to the combustion chambers to achieve higher compression ratios while permitting the use of very lean fuel-air mixtures, thereby permitting more efficient utilization of fuel, and resulting in minimization of undesirable emissions in the exhaust gases. This also enables the utilization of a low octane fuel, permits the engine to run cooler, and enables fast warm-up of the engine to the normal operating temperature. This improved internal combustion engine is thus desirable for use on vehicles since it permits the achievement of a higher power output from the engine, while at the same time providing for more efficient utilization of fuel.
In the improved engine of this invention, the turbocharger arrangement involves the use of first and second turbochargers, the turbine section of the first turbocharger being driven by a part of the exhaust gases from the engine, and the turbine section of the second turbocharger being driven by the remaining exhaust gases from the engine. The compressor section of the first turbocharger is used for supplying the air or air-fuel mixture to the intake manifold of the engine. The exhaust gases discharged from the turbine section of the first turbocharger are then supplied to the compressor section of the second turbocharger which compresses same and supplies these pressurized exhaust gases to the intake manifold for mixing with the air or air-fuel mixture therein. This pressurized mixture is then supplied to the combustion chambers so as to achieve a high compression ratio therein while possessing a minimum amount of fuel-air mixture due to the presence of the hot exhaust gases intermixed therewith.
Other objects and purposes of the invention will be apparent to persons familiar with internal combustion engines upon reading the following specification and inspecting the accompanying drawing.